Using people implies benefitting from people. People often use others to satisfy their selfish aims. But you can also use people in a positive way by learning and picking up things from them and also returning the favor when they need your help. This way, one can grow mutually by giving and taking from others, equally. If you only keep taking help from others and turn your back upon those people when they require aid, a time will come when you will be all alone and feel forlorn.
Man is a social animal and he needs others to grow and share his joy and sorrow with. This symbiotic relationship between people in which everyone uses the other person and tries to derive benefit in some or the other way is quite healthy. So, one should use people in times of need or when one feels that one can derive some benefit from the other person. But using people comes with a territory. You should be ready to offer help when others reach out to you.